Sunday, April 30, 2017

Vic Knows ‘Watt’ He’s Talking About

In the July 11th, 1944 episode, “Don’t Scrape off the Watts!” Sade buys Vic a new light bulb.  It’s supposedly super powerful (1 million volts).  Vic, being a gadget-guy, quickly opens the package and begins to examine it.   He cleans the contacts with his pocket knife.   There’s a lot of discussion about electricity in this episode.  Since I am an electrical engineer, it’s one of my favorites.    Let’s look at that light bulb from the perspective of an engineer.  I am reminded of the Chevy Chase quote, "It was my understanding that there would be no math.”  I know that this may be a dry subject, so I promise to keep the math to a minimum.  
There is a simple law that is the basis for all electrical engineering; it’s called Ohm’s Law.  You’ve heard the terms current, voltage, and resistance.  These terms are all related to each other via Ohms’s Law.  Before I describe Ohm’s Law, consider this analogy:  

You have a garden hose.  “Current” can be considered as the volume of water flowing from the hose.   “Voltage” can be equated to the water pressure.   Put your thumb over the nozzle of the hose and you have “resistance.”   Voltage, or water pressure, is generally fixed.  In the case of the hose, it is fixed by the height of your local water tower.  In the case of electricity, it’s fixed by your local utility.   As your thumb covers more of the nozzle, the resistance is increased and the volume of water coming out of the hose drops.  The same is true with electricity; the more resistance there is to the flow of the current, the less current that will be able to  flow.  

Ohm’s law describes these three concepts:   Voltage (volts) = Current (Amps)  * Resistance (Ohms)   Eqn 1

And electrical Power is simply:    Power (Watts) = Voltage (Volt)  *  Current (Amps)    Eqn 2

Changing any one the terms in these equations will result in the other terms changing as well, to keep the equations balanced.

In your home, the voltage at the outlets are fixed at 120 Volts.   What Vic is doing by cleaning the lightbulb’s contacts is reducing the resistance, since copper oxide is more resistive than copper.  If the resistance of the contacts goes down, and the voltage is fixed at 120V, then the current must increase to satisfy Ohm’s law (Eqn 1).  
With the current increased and the voltage fixed at 120V, the power dissipated in the bulb must be larger to satisfy Eqn 2.  More power results in a brighter light.  

Vic, per usual, knows exactly what he’s doing.  Cleaning the contacts will result in a brighter bulb.  Vic explains it better than I can, “I wanna make these contact points shine up good and bright, that way more electricity can get through an’ we’ll have a brighter light.”

Sade is completely lost on this topic and has no concept of electricity.  Sade’s lack of interest in learning about how things work (recall that she had no interest in understanding how her wash machine worked either) is disappointing to me, but I see this mindset frequently in my personal life.  Russel gets it, but his conversion from horsepower to Watts is inaccurate.  One horsepower is equal to 756 Watts, not 764 Watts.

This episode ends with a sort of sappy appreciation of Sade—maybe a little too sappy.  My mother, although not technically inclined, was always interested in learning and trying technical things.  I recall that she once attempted to work on her car and filled her radiator overflow reservoir with windshield washer fluid.  After realizing her mistake, my father convinced her that we’d have to turn the car upside-down to get it out!

-- Dave from Wisconsin
Wisconsin Professional Engineering License No. 26150-6

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